In general, aluminum cans have been used to contain beverages. However, in recent years, bottle-shaped cans with screw caps have been proposed. In general, the bottle-shaped can includes a large body, a shoulder whose diameter gradually decreases from a lower end to an upper end of the body, and a neck extending from the upper end of the shoulder upward, and a cap is engaged with a male screw formed on the neck.
The bottle-shaped can is formed by performing a DI process on a metal plate to form a cylindrical workpiece with a bottom, performing a necking process on an opening portion of the cylindrical workpiece several times to form a body, a shoulder, and a portion for forming a neck that is continuously connected to an upper end of the shoulder and extends upward, and performing, for example, a drawing process, a screw shaping process, and a curl forming process on the cylindrical workpiece.
In recent years, in order to appeal to consumers, this type of bottle-shaped can has needed to be changed so as to have various shapes with a high-quality design. In the related art, for example, printing or emboss processing has been used to manufacture the bottle-shaped can. The emboss process is disclosed in, for example, in JP-A-2004-123231 and JP-T-2000-515072.
JP-A-2004-123231 discloses the following method: a cylindrical mold having an inner circumferential surface that is formed substantially in the same shape as that of a shoulder, and a plurality of pressure portions, each extending substantially in the inclined direction of the shoulder, that are formed in the circumferential direction on the inner circumferential surface so as to protrude inward in the radial direction is arranged so as to coaxially face the opening portion of a cylindrical workpiece with the bottom; and, the mold and the cylindrical workpiece with the bottom are moved close to each other in the axial direction of the cylindrical workpiece with the bottom such that the opening portion of the cylindrical workpiece with the bottom is inserted into the mold and the pressure portions are pressed against the shoulder, thereby forming in the circumferential direction the plurality of grooves extending in the inclined direction of the shoulder.
JP-T-2000-515072 discloses the following method a first rotating body and a second rotating body are supported such that they can be rotated on their rotational axes parallel to each other; the first rotating body is arranged inside a cylindrical workpiece with a bottom and the second rotating body is arranged outside the cylindrical workpiece with a bottom; and the first and second rotating bodies are moved close to each other and are rotated on their rotational axes, with a body of the cylindrical workpiece interposed between outer circumferential portions of the first and second rotating bodies, thereby performing emboss processing on the body (forming convex and concave portions).
In the manufacturing method disclosed in JP-T-2000-515072, since the emboss processing is performed with the inner and outer circumferential surfaces of the body interposed between the first and second rotating bodies, it is possible to accurately form the concave and convex portions in the body. That is, when the body is interposed between the outer circumferential portions of the first and second rotating bodies, the convex portions formed in the outer circumferential surface of the second rotating body in the axial direction are fitted into the concave portions formed in the outer circumferential surface of the first rotating body in the axial direction with the body interposed therebetween. That is, metal forming the body is prevented from flowing in the circumferential direction, and the body is recessed inward in the radial direction. Therefore, the convex portions on the second rotating body can be accurately transferred onto the body.
However, in the manufacturing method disclosed in JP-A-2004-123231, the pressure portions of the mold are only pressed against the outer circumferential surface of the shoulder, but no pressure is applied to the inner circumferential surface of the shoulder, which makes it difficult to accurately form the grooves. That is, when the pressure portions of the mold are pressed against only the outer circumferential surface of the shoulder without pressing the inner circumferential surface of the shoulder, metal flow occurs in the shoulder in both the circumferential direction and the axial direction, which causes both portions of the shoulder pressed by the pressure portions and peripheral portions to be recessed to the inside of the body. As a result, it is difficult to form grooves having steep side walls in the outer circumferential surface of the shoulder and thus for the groove to be clearly viewed.
In order to solve the above-mentioned problems, the manufacturing method disclosed in JP-T-2000-515072 has been proposed in which a mold is also arranged inside the shoulder, and the shoulder is interposed between the mold provided inside the shoulder and a mold for pressing the outer circumferential surface of the shoulder. However, as described above, in a bottle-shaped can having a body, a shoulder that is connected to an upper end of the body and is tapered upward, and a neck that has a small diameter and extends from the upper end of the shoulder upward, it is difficult to arrange the mold inside the shoulder, and thus it is difficult to use this manufacturing method for this type of bottle-shaped can.